Preparing perennial garden for winter

Where did the summer go? It seems only a few weeks ago that we were potting up annuals and replanting the perennial beds. Yet this morning, as I look down on those beds from the porch, a chill in the air tells me that the end of the gardening season is not far off. The plants tell me this as well. The catmint patch, once a waving sea of blue buzzing with bees, is now green, its flowers gone. The penstemon stalks bear only seed pods and the pink is rapidly fading from the gay feather spikes, moving into the broccoli-like heads of the sedum. It is time to talk about putting those perennials to bed for the winter.

Most of my experience with herbaceous perennials was in Georgia, in the years before time became consumed with academic matters. Everything I know about perennial gardening in Maine I have learned as Marjorie’s apprentice, helping her prepare her garden for winter.

In autumn, as each variety of herbaceous perennial goes dormant, we cut back the dying stems, leaving a 2-inch stubble as a reminder of where the plants were growing, and pile the cuttings on the compost pile. We do not compost the top growth from any diseased plants.

The cutting-back is complete by early November. By Thanksgiving it is usually time to mulch the beds to hold the frost in the ground. The mulch protects the soil from intermittent freezing and thawing, forces that cause the plants to heave, exposing their roots to drying winds and killing cold. It is important not to mulch too early as this could allow the soil to warm enough for the plants to start growing again. Wait until the ground starts to freeze.

The best perennial garden mulch is a cover of pine, cedar or fir boughs. They are easy to put down and take off in the spring. We cut them fresh and lay them two layers thick over the tops of the stubble. They do a good job of catching and holding the snow, the best insulator against extreme winter cold.

Marjorie is a purist with regard to winter mulch. She says to avoid hay, which carries weed seeds, and straw, which is too difficult to clean up in the spring, leaving the garden beds looking untidy. She also avoids using leaves, which either blow away or mat, retaining excess moisture around the crowns and smothering the newly emerging spring growth.

We avoid cutting back the top growth of perennials that are decorative throughout the winter (see sidebar). For these varieties, we lay the conifer boughs around the plants as close to the stems as possible.

In April, as the ground begins to thaw, we remove the evergreen boughs and straw to let the sun warm the soil and start the process all over again. It is a process that reminds me how intimate gardeners are with the annual cycle of death and rebirth.

For the winter garden

. Astilbe (Astilbe sp.) – attractive dried seed heads on 3- to 4-foot stems.

. Coneflower (Rudbeckia sp.) – dried brownish-purple seed heads on 2-foot stems.

. Ornamental grasses – The dried flower look of tall grasses such as Feather Reed Grass (Calamagrostis acutiflora stricta) and Switch Grass (Panicum virgatum strictum) provide both winter interest and valuable winter cover for birds.

. Purple Coneflower (Echinacea purpurea) – dried mahogany-colored seed heads on 3-foot stems.

. Stonecrops (Sedum sp.) – Cultivars of Sedum spectabile such as ‘Brilliant’ and ‘Meteor,’ as well as hybrids such as ‘Autumn Joy’ and ‘Ruby Glow’, have dried flower clusters that are beautiful when dusted with new snow.

. Yarrow (Achillea sp.) – stiff, taupe-colored seed heads on 2- to 3-foot stems.

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